The invention relates to an aramid particle containing a peroxide radical initiator, to an aramid particle-elastomer composition, to skim products and mechanical rubber goods comprising the aramid particle, and to a method for vulcanizing a rubber composition.
In general terms adhesion systems for rubbers and other elastomers are known. For example, WO 95/22576 relates to an adhesion system for use with rubbers, synthetic elastomers and other unsaturated polymers. The system therein describes an adhesion system comprising an isocyanate compound, a polyunsaturated polymer and a plasticizer. Other materials may also be added to this adhesion system to perform other functions, for example a free radical initiator or generator can be added to facilitate bonding to the rubber and other polymers. This free radical initiator or generator will react with the other components of the adhesion system of this invention, either isocyanate or terminal or side groups on either polyunsaturated polymer. The added amount of free radical initiator is not disclosed, but to the skilled man it is known that the addition for such purpose involves low quantities of free radical initiator only. For example, in U.S. Pat. No. 3,484,333 and U.S. Pat. No. 3,674,542 sizing compositions for glass fibers are disclosed. The glass fibers are used as reinforcing materials for elastomers and plastics. The sizing comprises an elastomer and a hydrolyzable silane. According to the claims the sizing can contain from 1 to 6% by weight based on the unsaturated copolymer solids of a free-radical generating curing agent, such as a peroxide, which corresponds to only 0.1 to 0.6 wt % based on the weight of the fibers. In example 15 of U.S. Pat. No. 3,484,333 a glass fiber cloth is treated with a size containing 95 parts of toluene, 4 parts of butadiene-styrene copolymer, 1 part of silane, 0.08 parts of dicumyl peroxide and 0.08 parts of 2,5-dimethyl-2,5-di(t-butyl)peroxyhexane. Assuming a common sizing pick-up of 300 wt % with respect to the glass fiber, the sized glass fiber contains 0.4 wt % of peroxide on yarn after drying.
Such amounts of peroxide are common as is for instance also clear from U.S. Pat. No. 5,319,003 wherein a thermosetting mixture for coating continuous filaments is disclosed. The thermosetting mixture comprises unsaturated polyester or vinyl ester resin, styrene, and a strain relieving polymer. The thermosetting mixture can further contain a curing catalyst such as organic peroxide. The peroxide employed will generally range from about 0.1 to 4 parts by weight and preferably 1 to 2 parts by weight of the initiator per 100 parts by weight of the mixture of resin and strain relieving polymer. For instance, in Table 1 the amount of peroxide is 0.28% by weight, corresponding to 0.4 wt % based on the weight of glass fiber. Similarly, in U.S. Pat. No. 6,191,286 a size comprising an unsaturated imidosilane and a resinous medium is used, which size may include a free-radical generator, such as organic peroxide. The size is supplied to the inorganic solid material from about 0.01 weight percent to about 10 wt %, and preferably from 0.1 to 0.5 wt % based on the weight of the inorganic solid material. In Example 3 the glass fiber is first dipped in a 0.5 wt % silane solution and dried, and then dipped in a toluene solution containing 0.15 wt % dicumyl peroxide. Assuming a common sizing pick-up of 300 wt % with respect to the glass fiber, the glass fiber contains 0.45 wt % peroxide after drying.
Thus organic peroxides have been used in yarn sizing compositions to improve adhesion, however, the amounts used are not higher than 0.5 wt % of the weight of the yarn.